1. Technical Field
The present disclosure relates to display devices, and more particularly to a touch-enabled display device.
2. Description of Related Art
Various types of flat display panels, such as a plasma display panel (PDP), a liquid crystal display (LCD) panel, an organic light emitting diode (OLED) display panel and others, are commonly used with compact electronic apparatuses. Such flat display panels are very thin, provide high quality images, and consume minimal power.
The LCD device is particularly popular in the current market because of its lower cost. The LCD device generally includes a color filter substrate, a thin film transistor (TFT) substrate, and a liquid crystal layer sandwiched therebetween. A common electrode layer and a plurality of pixel electrodes are provided on the color filter substrate and the TFT substrate, respectively. Each pixel electrode, a part of the common electrode layer and liquid crystal molecules of the liquid crystal layer sandwiched therebetween form a liquid crystal capacitor. The liquid crystal molecules sandwiched between the common electrode layer and the pixel electrodes obtain different rotation angles under control of electric fields generated by signals provided to the common electrode layer and the pixel electrodes. Thus the LCD panel displays different gray levels at different pixels, with the pixels collectively forming an image viewed by a user.
To meet user requirements of intuition and convenience, various types of LCD with touch control function have been developed for display devices. In particular, there are in-cell touch display devices and out-cell touch display devices. The in-cell touch display device has attracted much attention. The out-cell touch display device requires an additional touch panel for detecting contact. The in-cell touch display device provides touch control function built into the LCD cell. No additional touch panel is required, and thus the in-cell touch display device has advantages of light weight, compactness and high optical performance. Most of the in-cell touch type display panels belong to the optical sensation type which has photo sensors formed at a same substrate with a TFT unit. That is, the photo sensors are provided at the TFT substrate. Each photo sensor serves as a detection element, and can for example be a diode or a transistor.
However, each detection element of the in-cell touch display device occupies a part of a corresponding pixel. In such pixel, the size of the pixel electrode is less than that of other pixel electrodes in other pixels. As a result, the capacitance of the liquid crystal capacitor formed in the pixel having the detection element is different from that of the liquid crystal capacitor in any other pixel not having a sensing element. Thus, when a scanning signal applied to the pixels changes between a high level signal and a low level signal, feed-through voltages of the pixels cannot be maintained constant, and flickering of the displayed image is generated. In addition, the above phenomenon not only occurs in the in-cell touch display device, but also occurs in other display devices that have pixel electrodes with different areas.
What is needed, therefore, is a display device that can overcome the above-described deficiencies.